This invention relates generally to a transducer assembly for measuring absolute pressure and more particularly to a miniature pressure transducer assembly and method using a diaphragm as a stress magnifying device which acts as one wall of a sealed pressure chamber.
Pressure transducers using hermetically sealed bellows or diaphragms are well known as means for indicating ambient pressure when associated with mechanical structure for monitoring diaphragm or bellows motion resulting from ambient pressure change. These transducers are relatively large due to the use of conventional welding processes which place a lower limit on the size of the parts to be welded together. Silicon strain sensitive resistive devices have been individually bonded to members stresses by pressure applied for providing resistance characteristics related to the pressure.
The need to obtain reliable pressure measurements in biological systems has been increasingly felt because of rapid advances in the biomedical field. The cardiovascular system, the cerebro-spinal system, the gastro-intestinal system, and the bladder are but a few of the places in the human body where pressure readings are often required. Detailed pressure recordings from the cardiovascular system are the most important, since, in combination with an ECG, they provide accurate diagnosis of the condition of the heart.
At present, the most common techniques for measuring intra-arterial blood pressure utilizes a flexible stainless steel guide wire about 1 mm in diameter which is inserted into the artery. This guide wire is pushed to the location where pressure is to be measured, while its progress is monitored using a fluoroscope. A hollow catheter which envelopes the guide wire is then inserted and pushed to follow the guide wire to the desired location. After next removing the guide wire and filling the catheter with a suitable fluid, the in vivo pressure can be measured by placing a pressure transducer at the end of the liquid-filled catheter, outside the biological system. This method has inherent limitations due to the long path that the pressure wave has to travel to reach the pressure sensor. The recorded pressure wave is a function of the propagation characteristics of the hollow catheter and can depart appreciably from the true in vivo pressure.
Ideally, to avoid this propagation distortion, a pressure sensor could be inserted into the catheter to replace the guide wire; however, due to the scarcity of pressure sensors with an outer diameter equal to or less than that of conventional guide wires, this method is rarely followed.
A need exists for pressure transducers having self-contained reference pressure and very small physical size, which may be obtained through the use of semiconductor materials and integrated circuit processes for providing greater efficiency in the use of available volumes for a pressure transducer.